The invention relates to a dry air filter for internal combustion engines of utility vehicles fitted with a system for generating compressed air, the dry air filter consisting of a filter housing containing a filter cartridge and preliminary dust-separator stage, which has an outlet with a discharge valve for the dust separated by the preliminary separator stage.
Dry air filters of the type described in U.S. Pat. No. 5,547,480, for example, are intended to deliver the requisite combustion air to the internal combustion engine as free as possibly from dust. To this end, any coarse impurities are firstly removed from the combustion air in the preliminary separator stage, after which fine dust is removed in the filter cartridge. The impurities arriving at a preliminary separator stage drop through an orifice in the housing wall at the end of this stage and into the outlet and are then either collected in a container or discharged to the open air via a dust discharge valve.
Dust discharge valves are described in HANDBUCH der MANN-FILTERTECHNIK, Section MANN-Trockenluftfilter, page 13. In specific situations (sudden high demand for power) due to the high vacuum pressure which then prevails, they prevent dust carried in the air from being sucked through the outlet. This air cannot be pre-treated by the preliminary separator stage or can be so only to an unsatisfactory degree, and this reduces the service life of the downstream filter cartridge intended for removing fine dust form the air.
Because of their structure, dust discharge valves are susceptible to clogging and are therefore not totally maintenance-free. The displacements of the discharge valve which occur due to the pulsing of the internal combustion engine during normal driving (rapid change in the vacuum pressure in the air filter) have a certain cleaning effect. However, they cannot prevent wet dust or larger harvest residues such as straw from sticking to the discharge valve and generally causing it to become blocked. As a result, it is necessary to clean the discharge valve manually from time to time. However, because the air filter is disposed under the engine bonnet, it is very difficult to assess, particularly in the case of large utility vehicles and cleaning of the discharge valve in due time often tends to be put off until there is a risk of the air filter becoming totally blocked. In addition, the system can also start to become clogged from the peripheral region of the opening in the filter housing, where coarse particles of dirt tend to adhere. In this case, cleaning the discharge valve manually will be of no help and the air filter has to be fully cleaned.
The objective of the invention is to design the air filter so that it will be easier to maintain this objective is achieved due to the fact that compressed air is delivered to the outlet, at least intermittently and, in order to produce an ejector action to keep the outlet and optionally the dust discharge valve closing off the outlet free of dust, is blown in the direction of the outlet of the dust discharge valve. As a result of the invention, the dust discharge valve is blasted with compressed air either continuously or at predetermined intervals, preventing a build-up of blockage in the outlet and the dust discharge valve. As a result, there is no need for separate, regular checks to ensure that the dust discharge valve is operating correctly and, as is the case, cleaning thereof. A system is already known in which an ejector effect is produced using the exhaust gases in the exhaust silencer of a motor vehicle and applied as a means of discharging dust. To this end, an exhaust silencer of this type (made by Eberspacher) has a terminal exhaust gas pipe, the inner end region of which is of a nozzle design in order to generate an under-pressure. In this region, the end of a long pipe projects into the dust to be removed. The dust is drawn out through the pipe due to the under-pressure and blown into the atmosphere with the exhaust gas. If the know system is rated to operate at full load, it works satisfactorily within this range. However, if the vehicle is operating at partial load or is idling, only a slight under-pressure is generated in the nozzle due to the small quantity of exhaust gas and there is a risk that the pipe carrying the dust will become blocked, in particular because of its length. If, on the other hand, the system is rated to operate at partial load, there is no risk of the pipe carrying the dust becoming blocked but when the system is operating at full load, a high counter-pressure builds up which significantly reduces the effective engine output. The invention provides a technically simple solution to the problem by delivering compressed air to the outlet and applying compressed air to the dust discharge valve, a line delivering the compressed air is run via a pressure-tight mounting through the wall of the outlet and has an end region facing the dust to discharge valve. In order to improve the ejector action, it has proved of practical use to deliver the compressed air to the outlet via a nozzle. In order to enhance the cleaning action of the blast of compressed air, it is also proposed that a nozzle be incorporated in the end region of the line and funnel-shaped hood, widening in the direction of the air flow, be provided, an annular gap being formed between it and the us outlet. For the same purpose, a nozzle may be provided immediately after the free end of the line, the flow direction of the compressed air leaving the line, the nozzle preferably comprising a venturi which acts to draw air and dust through the outlet.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.